test: remove string literal as message in strictEqual() in stream test

This reveals the values that cause the assertion error, should it
happen.

PR-URL: nodejs#30561
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

test/sequential/test-stream-writable-clear-buffer.js

@@ -26,9 +26,8 @@ for (let i = 1; i <= 5; i++) {
   testStream.write(i, () => {
     assert.strictEqual(
       testStream._writableState.bufferedRequestCount,
-      testStream._writableState.getBuffer().length,
-      'bufferedRequestCount variable is different from the actual length of' +
-      ' the buffer');
+      testStream._writableState.getBuffer().length
+    );
   });
 }